Geologic Publications for Mount Rainier

Geomorphology of Mount Rainier: Landform mapping at Mount Rainier National Park, Washington

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Author(s): Jon L. Riedel, Stephen Dorsch

Category: PUBLICATION
Document Type: Natural Resource Report NPS/MORA/NRR-2016/1234
Publisher: National Park Service
Published Year: 2016
Volume:
Number:
Pages: 162
DOI Identifier:
ISBN Identifier:
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Abstract:
The Geomorphology of Mount Rainier National Park (MORA) was completed as one of the 12 basic inventories desired for each park in the 1998 Natural Resources Challenge Inventory Program. It is closely linked to ongoing mapping of soils by the Natural Resource Conservation Service and to the multi-scaled USFS National Hierarchical Framework for Ecological Units (Cleland et al. 1997) to provide opportunities for ecosystem management with adjacent national forest lands.

In the broadest sense, the geology of MORA is a testament to the awesome power of tectonic forces near a subduction zone that created the largest stratovolcano in the lower 48 states. At a small scale (Subsection) Mount Rainier volcano is surrounded by mountains dominated by older volcanic rocks, setting it apart from Glacier Peak and Mount Baker to the north. The geomorphology of the park is also strongly shaped by surficial Earth processes that are controlled largely by climate, such as glaciation, mass wasting, and river erosion and deposition that are controlled largely by climate. These processes created the shape of the landscape adjacent to the volcanic cone that dominates the skyline for hundreds of miles and accounts for about 8% of the park.

Erosion by glaciers created the dominant landforms of the park, the cirque and valley wall. Slightly more than half of MORA is mapped as valley wall, while the heads of all major valleys are mapped as glacial cirques and account for 7% of the park. Glacial moraines are common landforms and are scattered at various elevations. The youngest of these moraines tower above the termini of modern glaciers and attest to the sensitivity of the glaciers to climate change. Only 100 years ago, glaciers filled the valleys above the moraines to cover about 30% more of the park than they do today.

Mass-wasting processes are important on the steep slopes of the volcanic cone and valleys walls. The largest landslides in the recent history of the park created the Osceola and Sunset amphitheaters on the volcanic cone, and triggered massive lahars that reached all the way to Puget Sound as little as 600 years ago. We also mapped 116 large landslides (debris avalanches) along valley walls; many of these are very old features, while many others remain active today. Rock falls and topples are also common from cliffs and rock summits across MORA. Most of the material being eroded from valley walls ends up at the bottom of these steep slopes to form debris aprons. This landform is the second most prevalent in the park, covering about 12% of the total area, and has a significant amount of volcanic ash from more than 30 eruptions of Mount Rainier and other Cascade volcanoes.

Five major watersheds radiate from the volcanic cone, and each has a somewhat unique geologic history. Because they head on the heavily glaciated active volcano, Cowlitz, Carbon, Nisqually, Puyallup and White rivers have broad glacial valleys with wide, terraced floodplains and braided rivers. They all have carried large lahars from the volcanic cone to surrounding lowlands. In contrast, the Ohanapecosh valley is the largest in the park that does not head on the volcano and, as a result, has a different geomorphology than the others. This is evidence by a higher proportion of valley walls (71% of basin) and a narrow floodplain that accounts for less than 1% of the watershed.

Most of the valleys have broad, U-shapes created by glaciers, but steep, rock-walled river canyons also occur throughout the park and include popular visitor destinations such as Box Canyon on the Muddy Fork of the Cowlitz River. In some cases the canyons are found down-valley from the reach of glaciers, while in other settings they are carved into the flat floors of glacial valleys.

Several unusual landforms were identified in this inventory. A sackung was identified along the west side of Iron Mountain in the Kautz Creek watershed. Sackungs are typically identified as depressions running near the crest of a ridge and are deep-seated slope failures driven by gravitational forces acting on valley-walls over-steepened by glacial erosion. Parklands are gently sloping former lava flows that are favored destinations for visitors because of their accessibility and beautiful open subalpine meadows. This inventory identified 55 individual parklands that cover about 29 km2 of MORA. Another noteworthy landform at MORA is patterned ground, which consists of stone lines or rock polygons created by frost action on fine-grained deposits at elevations high above treeline. We identified nine sites in the park with these features; all are found along high ridges where winter temperatures are extremely cold and high winds remove insulating snow cover.

The data contained in this report has several important management implications for MORA. Landforms provide critical information on three of five soil forming factors (parent material, time, and relief) and are also closely linked to vegetation. Combining landform, soils and vegetation data will allow park staff to unlock many key ecological relationships, identify habitat for key species of plants and animals, and guide ecological reference site selection and restoration. This report also presents important information for management of geologic hazards, including volcanic (lahars) and non-volcanic (rock falls, debris cones, debris avalanches). Many of the mapped landforms provide information on past climate change in the park; these include features which range from less than 100 years old to glacial moraines as old as the last ice age (13,000 years ago). Data included in this report will also assist with cultural resource management because landform age is known to correspond to the density of archeological sites. Finally, this report contains many stories about the natural history of the park that interpreters can share with the public. These stories include, but are not limited to, the history of the volcano and the unique natural history of each major valley, the sensitivity of the park to climate change, prehistoric human use of MORA, and the inter-relationships between geology, climate, geomorphic processes, soils, vegetation, and habitat.

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Suggested Citations:
In Text Citation:
Riedel and Dorsch (2016) or (Riedel and Dorsch, 2016)

References Citation:
Riedel, J.L. and S. Dorsch, 2016, Geomorphology of Mount Rainier: Landform mapping at Mount Rainier National Park, Washington: Natural Resource Report NPS/MORA/NRR-2016/1234, National Park Service, 162 p..